February 5, 2020 Subject:
The work does not appear to include a proper copyright notice. Prior to March 1, 1989 (this work was well before) notice of copyright was necessary on all published works. Without this notice, the work is in the public domain. After that date a copyright notice became no longer mandatory to protect a work.
This does not apply in most other countries however.
October 11, 2017 Subject:
Not Public Domain
The original author of this book died in 1988. This book is public domain nowhere except for perhaps Somalia, Marshall Islands, Libya and Yemen. Not trying to be a killbuzz, just saying that you can get into actual trouble distributing copyrighted material whether you do it for compensation or not.